、！！
But holding back your strikes during sparring isn't kindness!!
Literal
But, sparring [in-で] hand [obj-を] not-put-out [nominalizer-の] [topic-は] kindness is-not!!
A martial-arts instructor's insistence. 組み手 is the sparring practice in karate and related arts — not a full fight but controlled striking. 手を出す is a fixed idiom 'to lay a hand on / to strike / to attack,' though it can also mean 'to interfere in' or 'to touch' in other contexts. The 'のは ... ではない' cleft emphasizes 'the thing that ... is NOT X,' rejecting a misidentification. Double exclamation marks intensify the declarative force.